The disclosure relates to an image processing method for white balance. In particular, the disclosure relates to an image processing method capable of improving image quality by updating gain values according to reference division lines on a GRGB grid and performing bounding using the final gain value obtained according to the update.
Recently, as image technologies based on cameras and video devices have been developed, automatic adjusting technologies such as an automatic focusing (AF) scheme, an automatic exposure (AE) scheme, and an automatic white balance (AWB) scheme have been required to obtain superior image quality under various environments.
White balance is a process of removing unrealistic color casts so that an object, which is shown as a white object to a user, is represented as a white object in a photo or a picture.
A camera must perform the white balance by taking the color temperature of a light source into consideration, and the white balance depends on the relative coolness or relative warmth of the light source.
Human eyes can determine a white color under various light sources. However, digital cameras frequently have great difficulty with the auto white balance (AWB) because the human eyes and image sensors provided in the digital cameras make differences in characteristics and sensitivity thereof.
If the white balance is incorrectly performed, unsightly blue, orange, or even green color casts are caused. Accordingly, an unrealistic result, in extreme case, a fatal result may be caused in the picture.
For example, as the temperature of a light source is increased, a blue color is more expressed. In contrast, as the temperature of the light source is decreased, a red color is more expressed. The white balance refers to a technology, in which the balance between the blue and red colors is adjusted approximately to the color state of natural light so that the color distortion is removed.
Meanwhile, color temperatures represent the spectrum of light radiated from an ideal blackbody having the surface temperature, and represent the surface temperature calculated as numeric values.
The blackbody refers to an ideal object that only absorbs light, and neither reflects light nor transmits light. The range of the color temperatures may vary depending on the types of light sources as shown in following table 1.
TABLE 1ColorTemperatureLight Source1000-2000 KCandlelight2500-3500 KTungsten Bulb(household variety)3000-4000 KSunrise/Sunset(dear sky)4000-5000 KFluorescent Lamps5000-5500 KElectronic Flash5000-6500 KDaylight with Clear Sky(sun overhead))6500-8000 KModerately Overcast Sky